The present invention relates, in general, to chemical mechanical planarization (CMP) systems, and more particularly, to a pad conditioner coupling and end effector for a CMP tool.
Chemical mechanical planarization (also referred to as chemical mechanical polishing) is a proven process in the manufacture of advanced integrated circuits. CMP is used in almost all stages of semiconductor device fabrication. For example, chemical mechanical planarization allows the creation of finer structures via local planarization and for global wafer planarization to produce high density vias and interconnect layers. Materials that undergo CMP in an integrated circuit manufacturing process include single and polycrystalline silicon, oxides, nitrides, polyimides, aluminum, tungsten, and copper.
In general, semiconductor wafer polishing occurs on a rotating disk known as a platen. The rotating disk is a support structure for the polishing process. A polishing media is placed on the platen. The polishing media is compliant and allows the transport of a chemical/abrasive slurry. One type of polishing media is a polyurethane pad. The polyurethane pad includes grooves or indentations to promote slurry transport.
A polishing process begins with polishing slurry being applied to the polishing media surface. A semiconductor wafer is brought in contact with and coplanar to the surface of the polishing media. A predetermined force is applied to the semiconductor wafer to chemically and abrasively remove a portion of the surface of the processed wafer. Typically, the semiconductor wafer and the platen are rotated during the polishing process. Polishing slurry is continuously provided to the polishing media during the polishing process. Particulates from the semiconductor wafer and spent polishing slurry become trapped and build up as semiconductor wafers are polished. This results in the surface of the polishing media being non-uniform. The particulates can also scratch and damage the surface of the semiconductor wafer.
Pad conditioning is a process to remove particulates and spent polishing slurry from a polishing media. Pad conditioning also planarizes the pad by selectively removing pad material, and roughens the surface of the polishing media. Prior art, pad conditioning apparatus move an abrasive material across the surface of the polishing media. One commonly used pad conditioning apparatus includes a disk having a collet connected to an upper surface of the disk. An abrasive disk is adhesively or mechanically attached to a bottom surface of the disk exposing an abrasive surface. A coil cut is made in the collect to give the pad conditioning apparatus some angular compliance. A motor shaft connects to the collet of the pad conditioning apparatus. Rotating both the pad conditioning apparatus and the polishing media during a pad conditioning process achieves the best results. Typically, the pad conditioning process is performed after a series of wafers have been polished. In particular, the polishing media is conditioned after a wafer lot has been processed due to the time required for the operation.
Three problems arise from this style of pad conditioning apparatus. First, the coil cut in the collet of the pad conditioning apparatus is not effective in maintaining the abrasive surface parallel to the surface of the polishing media (angular compliance). The result is a non-uniform surface on the polishing media which directly impacts the semiconductor wafer polishing uniformity. For example, the pad conditioning apparatus could chatter during a pad conditioning process under certain operating conditions leading to high and low spots across the polishing media. Second, the downforce applied to the pad conditioning apparatus can completely close the coil cut into the collet, effectively obviating the compliance function with resulting loss of polishing pad flatness. Third, the pad conditioning apparatus periodically fails causing increased maintenance of the CMP tool. The downtime translates to increased cost and lower wafer throughput of the factory. The failure mechanism occurs when the abrasive surface catches an edge which places extreme torque on the coil cut collet. The collet eventually fails in tension and comes apart. The pad conditioning apparatus can come apart with such force that other components of the CMP tool can be damaged.
Accordingly, it would be advantageous to have a pad conditioning apparatus for a chemical mechanical planarization tool that has improved reliability in a manufacturing environment and increases polishing uniformity across a semiconductor wafer. It would be of further advantage if the pad conditioning apparatus was inexpensive and allowed easy replacement of the abrasive surface during normal maintenance.